World Expo Shanghai

The World Expo in Shanghai is being held from 1 May to 30 October 2010. Details are here:
http://www.worldexpochina.net/

Is it worth visiting? Can those who have visited the Expo share your experience? What is a good time to go?
The temperature in Shanghai is now 32 deg  Centrigrade, just like Singapore

Flashback:
I first visited Shanghai in1990. It was quite backward and under-developed. The transformation of Shanghai during the past 20 years was amazing, beyond imagination.